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    carrara68's Avatar
    carrara68 Posts: 10, Reputation: 0
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    #1

    Apr 11, 2009, 05:53 PM
    AC motor control on PSC with run capacitor
    Does anyone know what type of rheostat will slow a PSC motor with a run capacitor. It is a gear motor that final turn is 86rpm, but I don't know what the initial speed is. It is 110 volt and 2.1 amp. 60Hz When I hooked up a speed control I purchased on eBay, (and their ad stated that it would control a PSC motor) when I hooked it up the only thing it varied was the sound of the motor. No change in speed.

    Any insight would be appreciated.

    Will
    ceilingfanrepair's Avatar
    ceilingfanrepair Posts: 5,733, Reputation: 109
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    #2

    Apr 11, 2009, 07:13 PM

    See if your speed control has a trim pot. However I don't recommend using a solid state control on a gear reduction motor, it will probably stall out. You can try wiring a capacitor in series with the motor, or even a capacitor stepped control (like a 3 speed ceiling fan control from Lowes) but that too might stall out, or chew the gears.

    Gear motors are really designed to go at the speed they're designed to go.
    carrara68's Avatar
    carrara68 Posts: 10, Reputation: 0
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    #3

    Apr 11, 2009, 07:20 PM

    It did have a trimpot and only varied the sound again. This is a very burly motor, I doubt I could stall it, but what I am trying to turn has very little resistance. What is the difference between what I purchased and a Lowe's fan speed control? I would also like to hear more about the cap wired in series. Your input has helped the most, and I really appreciate it.

    Will
    ceilingfanrepair's Avatar
    ceilingfanrepair Posts: 5,733, Reputation: 109
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    #4

    Apr 11, 2009, 08:50 PM

    Solid state control is infinitely variable. Capacitor control has 3 or 4 distinct speeds i.e. high medium and low.
    carrara68's Avatar
    carrara68 Posts: 10, Reputation: 0
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    #5

    Apr 11, 2009, 09:02 PM

    If you don't know, don't bother replying
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #6

    Apr 11, 2009, 09:59 PM

    Three Ways to Control a Single-Phase Induction Motor - 2004-12-13 00:00:00 - Design News
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #7

    Apr 11, 2009, 10:19 PM
    This article http://powerelectronics.com/mag/506PET23.pdf sums it up fairly well:

    Low torque applications: Phase control works

    High torque applications (Yours): Need to move to VFD or Variable Frequency Drive
    carrara68's Avatar
    carrara68 Posts: 10, Reputation: 0
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    #8

    Apr 11, 2009, 10:25 PM

    It's a single phase motor, pay attention. Those articles are quite amusing.
    carrara68's Avatar
    carrara68 Posts: 10, Reputation: 0
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    #9

    Apr 11, 2009, 10:29 PM
    Sorry, you are correct.
    ceilingfanrepair's Avatar
    ceilingfanrepair Posts: 5,733, Reputation: 109
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    #10

    Apr 11, 2009, 10:33 PM
    Quote Originally Posted by carrara68 View Post
    If you dont know, don't bother replying
    What are you talking about? I answered your question.
    Tev's Avatar
    Tev Posts: 232, Reputation: 20
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    #11

    Apr 12, 2009, 04:41 PM

    There are basically two ways to change the speed of an AC motor. Alter the frequency or alter the number of poles. Here is the standard formula for AC motor speed.

    N=120f/P

    N=speed in RPM
    f=frequency
    P=number of poles

    120 is a constant and does not equal voltage, in fact, voltage does not enter into the equation. In other words, a rheostat will not alter the speed of an AC motor.
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